Desulfurization and sweetening process



Patented Jan. 17, lfifib DESULFURIZATION AND SWEETENING PROCESS Erving Arundale, Westfield, and John P. Thorn, Elizabeth,

N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application March 2, 1953, Serial No. 339,804

17 Claims. (Cl. 196-32) The present invention concerns a method for desulfurizing and/ or sweetening mixtures of hydrocarbons that contain compositions of sulfur. It particularly relates to a method of desulfurizing and sweetening a petroleum fraction which comprises treating the fraction with a mixture comprising an alkali metal carbonate or bicarbonate, an amine, and an aldehyde. It especially concerns the treatment of petroleum fractions that boil below about 700 F.

The existence of sulfur compounds in petroleum oils is well known in the art. Also well known is the fact that these sulfur compounds occur in virtually all of the hydrocarbon fractions that are derived from petroleum. The chemical structure of the various sulfur compounds is not very well known at the present time, but it is generally considered that they are largely (l) acidic compounds such as mercaptans and hydrogen sulfide, and (2) neutral compounds such as thiophenes, disulfides, alkyl and cyclic sulfides.

Regardless of their chemical structure, sulfur compounds are generally undesirable in all petroleum fractions and especially in those fractions that boil below about 700 F. These fractions include naphtha, kerosene, fuel oil, heating oil, gasoline, diesel fuel, etc.

Sulfur compounds, when they occur in a gasoline, tend to decrease the storage stability of the gasoline and to increase its tendency to form deposits within an internal combustion engine. They also generally have an adverse effect on the octane number response of a gasoline to the addition of tetraethyl lead.

in the case of kerosenes, it has been observed that the char value of a kerosene is often increased by the presenceof sulfur compounds. It has also been observed that sulfur, especially in the form of hydrogen sulfide or as a mercaptan, causes a hydrocarbon fraction to possess very undesirable odor and corrosion characteristics.

Accordingly, a number of desulfurization and sweetening processes have been devised to remove sulfur compounds from a petroleum distillate fraction or to convert them to less undesirable forms. The processes that are being used at the present time involve treating hydrocarbon fractions with materials such as sulfuric acid, sodium hypochlorite, copper chloride, sodium plumbite, caustic soda, bauxite, and the like. In general, desulfurization processes actually remove sulfur compounds from hydrocarbon fractions, while sweetening processes either remove mercaptans from such fractions or convert the mercaptans to polysulfides or other compounds. Thus, a sweetening process may or may not be a desulfurization process.

The present invention concerns a desulfurization and/ or sweetening process in which a sulfur-containing hydrocarbon fraction is treated with a mixture comprising an alkali metal carbonate or bicarbonate, an amine and an aldehyde. The present process is directed primarily toward the light and middle petroleum distillates including gasoline, naphtha, kerosene, diesel fuel, heating oil and the like. As mentioned earlier, the present invention embraces the treatment of distillate fractions that boil below about 700 F., and it is particularly effective in treating those fractions that contain mercaptan compounds.

Sulfur-containing hydrocarbon fractions that may be treated in accordance with the present invention may be derived from virgin or cracked stocks, and they may contain paraflinic, naphthenic, aromatic or olefinic compounds.

The treating mixture of the present invention comprises an amine, an alkali metal carbonate or bicarbonate, and an aldehyde. In general, it is desired that a sulfur-containing hydrocarbon fraction be treated with about 0.1 to 3 wt. per cent of an amine, 0.1. to 5 wt. per cent of an alkali metal carbonate or bicarbonate, and 0.05 to 1 wt. per cent of an aldehyde, said percentages being based on the hydrocarbon feed.

It is preferred that a sulfur-containing hydrocarbon fraction be treated with about 0.25 to 1.5 wt. per cent of amine, about 0.5 to 2.5 wt. per cent of alkali metal carbonate or bicarbonate, and about 0.1 to 0.5 wt. per cent of aldehyde. The carbonates or bicarbonates can be used in anhydrous form or in aqueous solutions of suitable concentration. Preferred aqueous solutions are those that are substantially saturated with respect to the carbonate or bicarbonate.

The amine component of the present treating mixture may be selected from the class of compounds consisting of the hydrocarbon-soluble monoand di-alkyl amines containing 1 to 10 carbon atoms in the molecule. Typical compounds include the hydrocarbon-soluble primary and secondary amines, diarnines, primary and secondary alkanol amines. The secondary amines or secondary alkanol amines are the preferred types.

Typical amines include dimethyl amine, diethyl amine, dipropyl amine, dibutyl amine, diamyl amine, methyl or ethyl amino ethanol, and the like.

Epecially preferred amines include dirnethyl amine, diethyl amine, and dibutyl amine.

Aldehydes suitable for use in the present process include the aliphatic saturated aldehydes, the aliphatic unsaturated aldehydes, and polymers of the aliphatic aldehydes such as paraformaldehyde and paraldehyde.

Preferred compounds include gaseous formaldehyde, Formalin (a 37% aqueous solution of formaldehyde), acetaldehyde, and paraformaldehyde. An especially preferred aldehyde is formaldehyde in the form of Formalin solution.

Suitable alkali metal carbonates in the present treating mixtures include the carbonates and bicarbonates of the alkali metals including lithium, sodium, and potassium.

Little is known concerning the mechanics of the process of the present invention, but one reaction which is be lieved may occur in this sweetening process is as follows:

C 2H5 G 2115 NaHCOz asomN CzHa 02115 where R is an organic radical and formaldehyde, diethyl amine and sodium bicarbonate constitute the treating mixture. The aldehyde may be used in excess of the above stoichiometric ratio.

The process of the present invention may be best understood by reference to the drawing illustrating one embodiment of the same.

Refering specifically to the drawing, a feed oil which for the purpose of illustration is assumed to be a crude petroleum oil is introduced into distillation zone 10 by means of feed line 1. Distillation zone 10 may comprise any number and arrangement of distillation stages. Temperature and pressure conditions may be adjusted within distillation zone 10 to remove overhead by means of line 2, hydrocarbon constituents boiling below the motor fuel boiling range. Hydrocarbon constituents boiling within the motor fuel boiling range may be removed from zone by means of line 3. Higher boiling fractions as for example, kerosenes, diesel fuel fractions and still higher boiling fractions may be removed from zone 10 by means of lines 4, 5, and 6, respectively.

The hydrocarbon fraction boiling in the motor fuel boiling range is condensed and passed to storage zone 20. This fraction is removed from storage zone by means of line 7 and may be washed with aqueous caustic or alkali metal carbonate solution in a conventional manner in zone 21 for the purpose of removing any hydrogen sulfide and acidic compounds.

The caustic-washed fraction then flows through line 8 into reaction zone 21 where it is mixed and treated with a treating mixture comprising an amine, an aldehyde and an alkali metal carbonate or bicarbonate in accordance with the present invention. Reaction zone 20 may consist of a conventional mixing vessel equipped with paddle stirrers, turbo-mixers, propellers and the ike. It may also consist of conventional orifice type mixers located directly in line 8. Reaction zone 20 may also be operated in either a continuous or batch-wise manner. In addition, the amine, aldehyde and alkali metal carbonate components may be added either separately or in unison. It is preferred that the amine be added to the oil first followed by the adehyde and the alkali metal carbonate.

The reaction in zone 21 may be carried out at temperatures up to about 100 C. and is preferably carried out at about 25 to 50 C, Reaction times of 2 to 60 minutes may be employed, but reaction times of about 2 to minutes are preferred.

The mixture produced in reaction zone 21 may be withdrawn through line 27 and introduced within settling zone 28 where it separates into two phases. The hydrocarbon phase is withdrawn through line 30, and the remaining material withdrawn through line 29. The latter material may be discarded or regenerated to recover the amine constituent.

Water or an aqueous solution of alkali metal carbonate or bicarbonate is introduced into line 30 by means of line 31 and is intimately mixed with the hydrocarbon fraction as by means of an orifice mixer 32 or an equivalent mixing device. The water or carbonate solution is intended to wash the treated hydrocarbon fraction free of amine, aldehyde and complex compounds that are formed in zone 21-.

The hydrocarbon fraction and wash solution are introduced into zone 35 .wherein an aqueous phase separates, which phase is withdrawn from zone 35 by means of line 36. The washed hydrocarbon fraction may be repeatedly washed and separated in this manner to produce the desired product in line 51. Alternatively, the washed fraction may be introduced within distillation zone via line 37. This latter step is especially desirable when the amine employed in the process has a boiling point that is below the boiling point of the hydrocarbon fraction treated. In this case, the amine passes overhead through line 41, is condensed in zone 42 and is withdrawn through line 43. The hydrocarbon product is withdrawn through line 52. In some instances, it may also be desirable to withdraw the latter product as a sidestream in line 53 or as an overhead through line 41.

It will be noted that in conventional desulfurization processes that employ sulfuric acid as the treating agent, it is generally necessary to operate a distillation zone such as zone 40 in a manner to take the hydrocarbon product overhead and to Withdraw certain condensation and polymerization products as the bottoms. This is necessary since sulfuric acid characteristically degrades part of the hydrocarbon fraction treated by forming sulfonates and the like. In this connection, it will be noted that the alkaline system of the present invention avoids degradation of this type. The present amine-aldehyde-alkali treating mixtures react with sulfur compounds present in the hydrocarbon fraction treated to form water-soluble complex sulfur compositions that may then be readily extracted from the fraction.

Example 346 grams (500 cc.) of West Texas prime cut naphtha (boiling range to 250 F. and possessing a copper number of 50) were placed in a one-quart pressure bottle. 3.4 grams of diethyl amine, 3.4 grams of Formalin solution and 5.0 grams of sodium bicarbonate powder were added to the naphtha and the mixture shaken for /2 hour at room temperature. The resulting product was washed with two 50 cc. portions of water, the water separated and the hydrocarbon layer filtered to remove water. The final hydrocarbon product possessed a copper number of 1.0, thereby indicating that a large amount of the mercaptans originally in the naphtha had been removed.

It will be noted that the copper number of a hydrocarbon fraction is numerically equal to the milligrams of mercaptan sulfur present in ml. of the fraction that will react with a standard copper ammonium sulphate solution. 0

It will also be noted that sulfur-containing hydrocarbon mixtures other than naphtha may also be treated in accordance with the present process. For example, distillate fractions such as naphthas, kerosenes, heating oils, diesel fuels and the like, are very suitable.

It has been stated earlier that the reaction which occurs between the treating mixtures and sulfur-containing feed stocks of the present invention results in the formation of two liquid phases. One of these phases is a hydrocarbon phase, while the second is'an aqueous phase. In some instances a third phase may also be present as caused, for example, by the presence of alkali in amounts over and above that capable of solution in the liquid phases. These and other variations may occur in practicing the present process without departing from the spirit or scope of the invention.

What is claimed is:

1. Process for refining a sulfur-containing hydrocarbon fraction which comprises contacting said fraction with a treating mixture comprising an alkali selected from the class consisting of the alkali metal carbonates and bicarbonates, an aliphatic aldehyde and a compound of the general formula N-H R.

where R1 is a radical selected from the group consisting of hydrogen, alkyl and hydroxy alkyl, and R2 is a radical selected from the group consisting of alkyl and hydroxy alkyl, and thereafter water washing the treated fraction.

2. Process for refining a sulfur-containing petroleum distillate fraction which comprises treating said fraction in a contacting zone with about 0.1 to 3 Wt. per cent of an amine selected from the class consisting of the hydrocarbon-soluble primary and secondary alkyl amines, alkanol amines and diamines in combination with about 0.05 to 1 wt. per cent of a hydrocarbon soluble aliphatic aldehyde and about 0.1 to 5 wt. per cent of an alkali selected from the class consisting of the alkali metal car bonates and bicarbonates, thereafterwater washing the treated 'fraction to remove water-soluble sulfur composi tions therefrom.

3. Process as defined in claim 2 in which the petroleum fraction is treated with about 0.25 to 1.5 wt. per cent of the amine, about 0.1 to 0.5 wt. per cent of the aldehyde, and about 0.5 to 2.5 wt. per cent of the alkali.

4. Process as defined in claim 2 in which the amine contains from 1 to 10 carbon atoms.

5. Process as defined in claim 2 in which the aldehyde is selected from the class consisting of formaldehyde,

.acetaldehyde, paraformaldehyde and formalin.

6. Process as defined in claim 4 in which the amine is Mamas 7. Process as defined in claim 4 in which the amine is a hydrocarbon-soluble secondary alkanol amine.

8. Process for removing objectionable sulfur compounds from a petroleum distillate which comprises contacting said distillate in a treating zone with about 0.1 to 3 wt. per cent of a hydrocarbon-soluble amine containing from 1 to 10 carbon atoms and selected from the class consisting of the primary and secondary alkyl amines, diamines and alkanol amines, about 0.1 to 5 wt. per cent of an alkali selected from the class consisting of the alkali metal carbonates and bicarbonates and about 0.05 to 1 wt. per cent of an aldehyde selected from the class consisting of formaldehyde, acetaldehyde, paraformaldehyde and formalin solution, passing the resulting mixture to a settling zone, withdrawing a hydrocarbon phase from the settling zone, washing the hydrocarbon phase with water in an amount sufiicient to extract any amine, aldehyde and complex sulfur compounds that are formed in said treating zone, and withdrawing the resulting washed bydrocarbon phase.

9. Process as defined in claim 8 in which the amine is a secondary alkyl amine.

10. Process as defined in claim 8 in which the amine is diethyl amine.

11. Process as defined in claim 8 in which the aldehyde is formalin solution.

12. Process as defined in claim 8 in which the amine is dimethyl amine.

13. Process as defined in claim 8 in which the water employed in the washing operation contains an alkali selected from the class consisting of the alkali metal carbonates and bicarbonates.

14. Process for desulfurizing a sulfur-containing distillate hydrocarbon fraction boiling below about 700 P. which comprises contacting said fraction at about 25 to C. and for about 2 to 60 minutes with about 0.1 to 3 wt. per cent of an amine in combination with about 0.1 to 5 wt. per cent of an alkali and about 0.05 to 1 wt. per cent of an aliphatic aldehyde, said amine containing from 1 to 10 carbon atoms and being selected from the class consisting of the hydrocarbon-soluble primary and secondary alkyl amines, diamines and alkanol amines, said alkali being selected from the class consisting of the alkali metal carbonates and bicarbonates, thereafter water-washing the contacted fraction to remove water-soluble sulfur compositions therefrom.

15. Process as defined in claim 14 in which the alkali is in anhydrous form.

16. Process as defined in claim 14 in which the alkali is in the form of a saturated aqueous solution.

17. Process as defined in claim 14 in which the amine is diethyl amine, the aldehyde is formalin and the alkali is sodium bicarbonate.

References Cited in the file of this patent UNITED STATES PATENTS 

1. PROCESS FOR REFINNING A SULFUR-CONTAINING HYDROCARBON FRACTION WHICH COMPRISES CONTACTING SAID FRACTION WITH A TREATING MIXTURE COMPRISING AN ALKALI SELECTED FROM THE CLASS CONSISTING OF THE ALKALI METAL CARBONATES AND BICARBONATES, AN ALIPHATIC ALDEHYDE AND A COMPOUND OF THE GENERAL FORMULA 